The present invention relates to automatic or semiautomatic multiple-spindle machine tools in general, and more particularly to improvements in camless programoperated multiple-spindle machine tools wherein several workpieces can be treated simultaneously by tools mounted on cross slides or side slides.
It is already known to provide a multiple-spindle machine tool with a carrier which is indexible in a headstock of the machine frame and supports several parallel rotary work spindles. The carrier can be indexed between several positions in each of which different spindles are located at two discrete working stations where the workpieces are subjected to different treatments by one or more tools while being held by the chucks or analogous work-gripping portions of the spindles. As a rule, or at least in many instances, the treatment of a workpiece at one of several working stations takes up more time than the treatment of a workpiece at another working station; therefore, the intervals at which the carrier is indexed are determined by the longest period which is needed to complete the removal of material from a workpiece at a particular station. The periods of time which are needed to treat workpieces at several discrete working stations are different when the workpieces are treated in an automatic of the type disclosed in U.S. Pat. No. 3,643,307 to Ledergerber et al. This patent discloses an automatic wherein the carrier supports four work spindles two of which are located at working or material removing stations and two of which are located at additional stations where the workpieces are inserted, finished workpieces removed and partially treated workpieces transferred with simultaneous turning end-for-end.
It was already proposed to reduce the differences in the length of periods which are needed to treat workpieces at different working station in a multiple-spindle automatic. Such proposals include the making of deeper cuts and/or increasing the rate of feed at the time a tool engages a workpiece. However, the just described mode of machining workpieces results in excessive wear upon the tools and reduces the accuracy and reproducibility of treatment.